It is known in the art to use an abradable material in a rotating machinery application to form a good seal between a moving and a stationary part. This result is obtained by permitting one part to cut a channel or groove into the abradable material. In a gas turbine engine the abradable material is usually placed on the stationary case and the rotating blades cut a groove into the abradable material. In this fashion the changes that may result from thermal growth and blade creep are accommodated. Abradable materials are often located and restrained by being placed in a supporting honeycomb structure.
A typical patent which discloses an abradable material is U.S. Pat. No. 3,879,831. The contents of this patent are incorporated by reference. This patent discloses an abradable material having a total composition (by weight) of 60-80% Nickel, 2-12% chromium, 1-10% cobalt, 4-20% aluminum and 3-15% inert material such as diatomaceous earth, boron nitride, silica glass, mica, vermiculite asbestos, molybdenum disulfide, graphite, cobalt oxide, cerium oxide and zinc oxide. Up to 3% of a metal selected from the group consisting of yttrium, hafnium and lanthanum may also be added. Table 1 in the patent lists the abradable material components and the preferred particle sizes. Coated diatomaceous earth which is referred to is a product of the Sherrit-Gordon Corporation consisting of diatomaceous earth which has been coated with nickel or an alloy of nickel and chromium.
Similar teachings are found in U.S. Pat. No. 3,817,719 which is also incorporated herein by reference. Such known abradable materials have been applied to honeycomb structures by mixing the dry constituents with a liquid binder such as cellulose nitrate to form a paste and then packing the material into the honeycomb cells. With this method of applying the material to the honeycomb structure various difficulties have been encountered. The uniformity of application is quite variable; consequently, when a complete filling of the cells is desired, it may not be consistently achieved. The results depend to a large extent on the skill of the operator. Further, for those applications which require a partial fill of the honeycomb cells, so that only the bottom half of the cells contain the abradable material, this technique is not capable of producing the desired results.